Radiation therapy, or radiotherapy, is the medical use of ionizing radiation to control malignant cells. In intensity-modulated radiation therapy (IMRT), the intensity or segment of the radiation is modified in accordance with a treatment plan to deliver highly conformal radiation doses to the planning target volume (PTV) of malignant cells, while sparing the surrounding organs at risk (OARs) and other healthy tissues from radiation damage. By dividing the PTV and OAR volumes into individual volume elements (or “voxels”), the IMRT treatment plan can be characterized by a three dimensional dose distribution that characterizes the magnitude of radiation at each of the voxels. Another effective, two dimensional representation of the dose distribution is the dose volume histogram (DVH). Many clinical toxicity data and guidelines relating radiation damage to organs and radiation dose are expressed in DVH parameters (i.e., x1% volume, or x2 cc volume exceeding y1% or y2 Gy of dose).
A plan is Pareto optimal if it is impossible to further improve a certain dosimetric parameter without compromising the other parameters. Pareto optimal plans can include a set of plans that satisfy different planning criteria and objectives. The term intensity-modulated radiation therapy (IMRT) treatment plan (or simply “IMRT plan”) hereby includes all forms of treatment plans that utilize radiation treatment processes in which radiation intensity can be delivered in a non-uniform manner, including but not limited to: intensity modulate radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), treatment plans designed using TOMOTERPAY™, ACCURAY™, proton therapy, VIEWRAY™, VERO™, etc.
The development of an intensity-modulated radiation therapy (IMRT) treatment plan (or simply “IMRT planning”) typically involves a complex optimization procedure by which the radiation beam angles and strengths are designed to achieve required dose of radiation for the planning target volume as prescribed, as well as limit the radiation delivered to neighboring normal tissues. While a portion of the IMRT planning process may be performed via computerized optimization algorithms, typically much of the process requires the input and expertise of a human planner. The computerized optimization algorithm calculates the current-state dose distributions/DVHs of each PTV and OAR, and compares those values to the input dose/DVH objectives. The differences of these two sets dose/DVH values are used to adjust the strength of each radiation beamlet based on pre-determined formula.
In particular, the human planner is typically responsible for manually adjusting input planning dose objectives (e.g., dose limits, dose volume histogram [DVH] limits, etc.) via a time-consuming, iterative trial-and-error process. The trial-and-error nature of the process is due to the fact that the planner does not know whether or not a set of given dose objectives will result in a plan that meets all physician-prescribed goals for sparing organs at risk (known as “sparing goals”), or when it does, whether tradeoffs between planning target volume (PTV) coverage and sparing of organs at risk (OARs) can be further improved.
Further compounding the process is the fact that physician-prescribed sparing goals are often adapted from clinical trial studies for general populations (e.g., the Radiation Therapy Oncology Group's (RTOG) sparing goals, the QUANTEC (Quantitative Analysis of Normal Tissue Effects in the Clinic) toxicity data, etc.) that ignore specific anatomical, geometric, and demographic information for individual patients, and often represent the upper limit of an organ's dose tolerance rather than an individual patient's lowest achievable dose in that organ. In summary, because of the lack of quantitative tools for linking variations in anatomy to variations in OAR sparing doses, planners must rely on personal experience and expertise when making adjustments for individual patients. Further, because of the lack of quantitative tools for providing trade-off options between various PTV coverage objectives and OAR sparing objective, physicians and planners must rely on personal experience and expertise when making treatment decisions for individual patients. It is noted that trade-off options may be discrete or continuous, meaning there may be two or more trade-off options made available to a user.
For at least the aforementioned reasons, it is desired to provide improved systems and techniques for radiation therapy decision making and radiation therapy treatment planning.